1. Field of the Disclosure
The present disclosure relates generally to Internet protocol (IP) multimedia subsystem (IMS) call initiation, and more particularly, to methods and apparatuses for triggering an IMS call or a circuit switch fall back (CSFB) call based on a state of the user equipment (UE).
2. Description of the Related Art
The introduction of the IMS has significantly impacted wireless network equipment and their deployment. The IMS and the deployment of long term evolution (LTE) have had a significant effect on the operation of UEs. Further, the problems resulting from IMS deployment on UEs has not been completely explored from a non-access stratum (NAS) perspective. From the NAS perspective IMS call triggers in abnormal states must be considered, and include, for example, initiating by a tracking area update (TAU) request or a service request, the attempting-to-update in a UE, when timer(s) T3411/T3402/T3430/T3440 are running, and when TAU_INITIATED and TAU Reject with Temp causes network failure/congestion.
According to an existing method and system, as shown in FIGS. 1A and 1B, FIG. 1A illustrates an activity diagram illustrating an IMS call drop scenario at a UE which incorporates a single subscriber identity module (SIM) and dual SIM, according to the prior art.
In step 102a, once the LTE NAS layer is in a registered state with a network, the UE initiates a call request, such as, for example, a voice over LTE (VoLTE)/IMS call with the network. Further, in step 104a, the UE transmits session initiation protocol (SIP) data and uplink (UL) data packets to the network (i.e., NAS data plane). Thereafter, in step 106a, the UE transmits a request to NAS control plane, with the request, for example, switching from an NAS idle mode to NAS connected mode. In step 108a, the UE detects abnormal states in the NAS layer (i.e., NAS layer at the UE). The abnormal states include, for example, ATTEMPTING_TO_UPDATE the NAS, timer T3411 running, T340 running, and TAU_INITIATED and TAU reject with Temp causes like network failure, congestion, etc. Thus, due to this abnormal service state (i.e., evolved packet system (EPS) mobility management (EMM)) at the NAS layer, the UE sends no response message to the network. In step 110a, the UE may receive a drop/delay the IMS call/CSFB call indication from the network due to time out.
Thus, the unwanted SIP packet transfer of queued data even after the IMS call has timed out may cause confusion in the network and lead to the call drop.
FIG. 1B illustrates another activity diagram illustrating an IMS call drop scenario at a UE which incorporates a multi SIM, according to the prior art.
In step 102b, the UE triggers the recovery procedure, such as local area identity (LAI) using SIM-2 before initiating the IMS call by a SIM-1 of the UE. In step 104b, the SIM-2 acquires a radio frequency (RF) stack to perform the recovery procedure (such as performing local area update (LAU)). In step 106b, the LTE NAS layer (i.e., associated with the SIM-1) is in a registered state with a network, and the SIM-1 of the UE initiates a call request, such as, for example, a voice over LTE (VoLTE)/IMS call with the network. Further, in step 108b, the UE transmits session initiation protocol (SIP) data and uplink (UL) data packets to the network (i.e., NAS data plane). Thereafter, in step 110b, the UE transmits a request to NAS control plane, with the request, for example, switching from an NAS idle mode to NAS connected mode. In step 112b, the UE transmits a connection establishment request (i.e., associated with the SIM-1) to an LTE-AS.
As the RF stack has been utilized by the SIM-2 in performing recovery procedure, signaling, or other high priority activity, this may result in a poor user experience due to the lack of prioritization in a dual SIM dual standby (DSDS) UE and the unavailability of the RF for the SIM-1 that is triggering the IMS Call.
In step 114b, the UE may receive drop/delay the IMS call/CSFB call indication from the network due to time out.
This problem applies to two-receiver-DSDS (2RX-DSDS) if the second stack is busy in high priority UL activity. Similar problems (e.g., call drop, delay in establishing a voice call, and the like) persist in a dual SIM dual active (DSDA) UE.
In case of the DSDS UE, as since a VoLTE call is a packet switched (PS) call, and when circuit switched (CS) paging is received on a second SIM, there is a possibility that the VoLTE signaling may be interrupted since a modem may not be able to distinguish between a voice call and an ongoing video call. Hence, the VoLTE call may be disconnected and a default priority may be given to the CS call, continuing the poor user experience.